Among chemical methods of sterilization, the use of hydrogen peroxide and peracetic acid is acquiring considerable prominence. This is due to their bactericidal, sporicidal, and fungicidal properties, which have been known for many years (BAULDRY, M. G. C., The bactericidal, fungicidal and sporicidal properties of hydrogen peroxide and peracetic acid, Journal of Applied Bacteriology, Oxford, Vol. 54, pp. 417-423, 1983). Peracetic acid is used in aqueous solutions, as a vapour or spray, and is efficient in the sterilization of plastic packaging (RAMMERT, M., Aseptic cold fill: Experiences and developments, Industrie delle Bevande, Dreux, Vol. 25, No. 142, pp. 123-128, April 1996) and the disinfecting of industrial equipment, and is of particular interest in the food industry since it leaves a residue consisting of acetic acid, oxygen, water, and hydrogen peroxide.
There are commercial systems for sterilization, such as:    a) The Contitherm System, which applies hydrogen peroxide in the form of vapour which adheres to the surface in the form of a fine film of condensate, being activated with sterile hot air, as well as promoting the elimination of its residue;    b) The Freshfill System, which uses the sanitizing agent in the form of a spray. Jets of sterile hot air activate the peroxide and eliminate the residue; c) The Serc System uses a mixture of chlorinated water, hydrogen peroxide, and peracetic acid. The material remains in contact with the sanitizing agent for about 90 seconds. This is followed by rinsing with sterile water; d) The ethylene oxide sterilization system (ETO), largely used for sterilizing heat-sensitive materials with a high degree of penetrability of the materials, which requires heating up to 58° C. and can also use Freon gas in the process.
Despite the high diversity of the sterilization systems which use peracetic acid and hydrogen peroxide and ethylene oxide, there are still a number of problems of operational and financial nature, as well as risks of contamination of the materials and the environment during the process. For example, application in diluted form requires large volumes of the sanitizing liquid, the materials cannot be packed, and sterile water is required for the rinsing, as well as a clean area for drying, thus incurring in the risk of re-contamination.
If applied in the form of vapour or spray, the system requires air which is filtered, hot, and sterile, in order to activate and eliminate the residues. These systems incur high energy consumption, as a function of the use of heater devices. The process with ethylene oxide requires long periods of sterilization, as well as aeration, since this substance is highly toxic.
Sterilization with plasma is one of the most recent techniques for the sterilization of surgical instruments and represents a great number of advantages over the procedures referred to heretofore.
The plasma state of the material is obtained by means of electrical discharge in a high-voltage field, DC, AC, or pulsed, in gases at low pressure. The action of this field on the gas or vapour molecules results in the provision of sufficient energy to the charged particles (electrons and ions), and these begin to produce pairs of electron-ions as a result of collision with the neutral gas molecules. As a consequence, the formation takes place of ions, accelerated electrons, neutral types, free radicals, and excited atoms and molecules, as well as the emission of ultraviolet radiation. If the application of the field is stopped, the activated types recombine, forming other types or returning to their basic state.
One commercial application of sterilization by plasma is described by the STERRAD® system. In this process, the materials are placed in a chamber in which a vacuum is then created. A solution of hydrogen peroxide is injected and vaporised inside the chamber containing the items which are to be sterilized. After allowing for a certain amount of time for diffusion, the pressure in the chamber containing this vapour is reduced and a plasma is initiated, with radio frequency energy being provided in order to exterminate micro-organisms and remove residues. The process is completed by disconnecting the RF energy and admitting filtered gas (HEPA) into the chamber.
The Patent PI 9708498-0 (U.S. Pat. No. 628,965), entitled “Method of Sterilization in Environments with Restricted Diffusion” makes use of hydrogen peroxide vapour as the former material and electrical discharges by radio frequency to generate plasma. In this process, the articles which require sterilization in a restricted diffusion environment are exposed to a source of peroxide, which may be static flooding, spraying, condensation of hydrogen peroxide vapour or peracetic acid vapour, before exposure to a vacuum or in a vacuum followed by plasma. The difficulty with penetration of the hydrogen peroxide in the environment with restricted diffusion is due to the presence of water vapour which, because it reaches the area concerned first, has a higher vapour pressure, which turns it into a barrier to penetration by the hydrogen peroxide vapour.
The Patent PI 9504382-9 A (U.S. Pat. No. 320,932), with the title: “Method of Sterilization under Vacuum, Method of Evacuation of a Condensed Material, and Method of Drying”, describes a method of drying under vacuum with the liquefaction to plasma of residual gas and sterilization by the injection of sterilizing gas and a radio frequency source applied for the generation of plasma with the sterilizing gas. After a period allowed for diffusion in the sterilization process, the sterilizing gas, which is highly oxidant, is evacuated from the chamber by a vacuum pump in order to obtain lower pressure levels and to generate a plasma from this vapour, excited by an RF source.
The methods represented in the commercial systems and patents referred suffer from the following disadvantages:
1. The electrical discharge with radio frequency (RF) for the excitation of the plasma requires impedance couplers in order to obtain better utilization of the power supplied to the plasma. Depending on the geometric shape of the electrodes and the articles which are to be sterilized, this coupling may prove difficult, and consequently incur losses of energy and heating of the source, as well as the cost of the RF source being increased excessively with the increasing of its power, so making the sterilization processes substantially more expensive;
2. Damage to the vacuum system, incurred by the action of highly reactive gases during the process of evacuation after the exposure period and the diffusion of the sterilizing gas. This consequently requires a substantial number of handling procedures in the vacuum system, and a reduction in the service life of these items of equipment; and
3. Inefficiency of the process of sterilizing areas of restricted diffusion due to the injection of the aqueous solution of hydrogen peroxide or peracetic acid in the plasma sterilization system. Due to the physical properties of the water, this is diffused such that in the first instance it dilutes the concentration of the sterilizing vapours in the areas with restricted movement.